What was especially interesting were the psychology behind some well-known headline formulas and what makes them so clickable. Here’s an overview of eight winning headline formulas and the psychology behind them:

Surprises are more stimulating and will get our attention much more easily than things we already know well—even if we really like those things. We may subconsciously prefer an unpredictable experience over what we think we want.

One example of surprise would be the email subject lines of Barack Obama’s presidential campaign. Anyone who shared an address with the campaign got messages from Barack Obama with subject lines like “Hey,” “Wow,” or “Join me for dinner?”

Dropping in curse words like “Hell yeah, I like Obamacare” also got big clicks. Most of the $690 million that Obama raised online came from these fundraising emails. These emails worked because they created a surprising dissonance between Barack Obama and email subject lines that looked as if they had come from a friend.

2. Questions

Questions are powerful because they pique curiosity. Simply seeing a question mark stimulates your brain. If you already know what you’re going to get from a headline, your curiosity might be over before it can even start.

The best question headlines ask something the reader can empathize with, relate to, or would like answered. Consider this one by Bill Jayme in Psychology Today:

Note how your brain springs into action as you think about your answer and wonder how it compares against other people’s answers.

3. Curiosity

Upworthy has gained millions of clicks by taking advantage of a psychological phenomenon called the curiosity gap.

George Loewenstein, a professor at Carnegie Mellon University, coined this term to describe the gap between what we know and want to know. When we notice a gap in our knowledge, we feel deprived. We look for that piece of missing information to ease that feeling.

Curiosity requires some initial knowledge. We’re not curious about something we know nothing about, but as soon as we know even a little bit our curiosity is piqued and we want to learn more. Research shows that curiosity increases with knowledge—the more we know, the more we want to know.

A Cal Tech study scanned volunteers’ brains while they read trivia questions designed to create a mixture of high and low curiosity. When subjects were interested in a question, the researchers saw more activity in the caudate region—a part of the brain that anticipates rewards. (Interesting side note: If subjects found out they gave an incorrect answer, the curiosity effect seemed even stronger.)

To use this strategy in headlines, share some intriguing but incomplete information. Tell the reader enough to pique his curiosity, but not enough to give the whole story away. This famous ad by John Caples does this well:

Created in 1926, the ad went on to become one of the most popular and successful ads in history. Scott Delong, the founder of viral content site ViralNova, has it framed in his office.

The ad doesn’t sell piano lessons; it intrigues with the emotional benefit of learning a new skill.

4. Negatives

Superlatives—words such as “best,” “biggest,” and “greatest”—can be effective in headlines, but negative superlatives (like “worst”) can be even more powerful.

In a study of 65,000 headlines, Outbrain compared positive, negative, and no superlative headlines. The study found that headlines with positive superlatives performed 29 percent worse and headlines with negative superlatives performed 30 percent better. The average click-through rate on headlines with negative superlatives was 63 percent higher than positive ones.

There are a few theories on why this might be:

Positive superlatives have become clichéd through overuse.

Negatives are more intriguing because they’re unexpected and surprising.

Negatives tap into our insecurities. Using negative words like “stop,” “avoid” and “don’t” work because everyone wants to find out if there’s something they’re doing that they should stop.

Somewhat related is a finding from a Startup Moon study of 100 tech blogs that found that aggressive or violent-sounding words like “kill,” “dead,” and “fear” actually encouraged more social shares.

A lot of advertising writers say that if you start with the words “how to,” you can’t write a bad headline. After all, we all want to be smarter.

Copyblogger say these types of headlines go beyond knowledge to work on an even deeper level:

“Most people don’t want information. I know you’ve always been taught otherwise, but it’s true. People are drowning in facts. What people really want is a sense of order and predictability in their lives. We want to feel a sense of power over our world. Therefore, we seek out the secrets, tips, hints, laws, rules, and systems that promise to help us gain control and make sense of things.”

Witness the incredible staying power of one of the most famous how-to headlines: “How to Win Friends and Influence People” by Dale Carnegie.

Even with this proven formula, there are a few tweaks we can make to ensure our headlines spread.

A Startup Moon tech blogs headline study found a huge difference between the viral spread of a post titled “How to use Android SDK” and another titled “The beginners guide to Android SDK.” It’s the same concept, but different packaging. Adding words like “Introduction,” “The beginners guide,” “In 5 minutes” and “DIY” can provide more viral variations on the how-to headline.

This tells us you might want to work something specific into your headline to give readers a better idea of what they’re going to get. For example, instead of “How to get better at organizing your day,” you might try, “The 5-minute guide to organizing your day for more focus and productivity.”

If a patient in a waiting room is told the doctor is running 30 minutes late, the patient might be annoyed but will eventually relax into the wait. However, if the patient is told the doctor will be ready soon, the patient is nervous and unable to settle down because he thinks he’ll see the doctor soon. When we’re in this situation, time feels as though it moves more slowly.

Numbers manage expectations for us—they tell us exactly what we’re getting into. That might be why a Conductor study found that audiences prefer number headlines to almost any other type.

Additionally, the Startup Moon headline study found that the bigger the number, the farther the post spreads.

7. Audience referencing

Audience referencing basically means using the word “you,” or directly implicating your audience with your headline. Copywriter Mel Martin was known for this. He would write headlines like “For golfers who are almost (but not quite) satisfied with their game—and can’t figure out what they’re doing wrong,” and this similar variation:

This headline type gets attention because of the way our brains fixate on solving problems. It’s part of our survival instinct for our brains to actively search for potential problems—even if they’re as minor as a golf swing or cooking. When you are the precise target audience for a headline, your brain says, “That’s for me!”

In a Norwegian study, researchers tried a variety of headline styles on a shopping website:

“For sale: Black iPhone4 16GB” (the regular headline)

“Anyone need a new iPhone4?” (question headline without referencing cues)

“Is this your new iPhone4?” (question headline with referencing cues)

Researchers found that question headlines with audience-referencing cues (“Is this your new iPhone4?”) produced higher click-throughs than other headline types.

Even if you don’t use the audience-referencing strategy, keep in mind how strong human self-interest is. When you speak to the desires, needs and emotions of your reader, you answer their main question: “What’s in it for me?”

8. Specificity

Another principle that makes ideas stick, according to Chip and Dan Heath, is to use specific facts rather than broad statements.

Specific, quantifiable facts—particularly those that evoke mental pictures—are intensely interesting. Figures imply research, which adds to your legitimacy, but all kinds of specificity are good: digits, names, descriptions, titles, examples, projections, results. Being specific also demonstrates that the article will be in depth.

Being specific appeals to our urge to know what we’ll get when we click, and leads to greater clarity. Readers prefer clarity, as you can see in this Conductor study:

It’s also worth noting that the folks at Upworthy, who were previously high on curiosity-gap headlines, are now finding that descriptive headlines—headlines that tell you exactly what the content is—are starting to win out over curiosity-gap headlines that tease you by withholding details.

Curiosity-gap headlines used to work because people weren’t used to them, but they’re now common.

As you try these strategies, you may find that one headline type works really well for a while, and then begins to show diminishing returns. The key is to keep finding new ways to engage your audience. Be playful and experimental with what you write—and ruthless with how you test.

What headline strategies produce results for you? Please share them in the comments.

Courtney Seiter creates content at Buffer. A version of this article originally appeared on the Buffer blog.